Decorative paper layer, printable paper layer, method for manufacturing a printable substrate, and ink used in the method

Abstract

A decor paper ply comprising a base paper ply and a pattern formed by digitally applying ink to at least one surface of the base paper ply, characterized in that the depth of penetration of the ink from the surface into the core of the base paper ply is less than 30% of the thickness of the base paper ply. The invention also relates to a method for manufacturing printable paper and decor paper ply, and to an ink for use in such a method.

Description

Technical Field

[0001] This invention relates to a decorative paper layer in a method for manufacturing a panel or so-called decorative panel with a decorative surface, and to the ink used in the method. The invention also relates to a method for manufacturing printable paper or another substrate using inkjet printing, for use as decorative paper in, for example, such panels, and to printable paper obtainable by such methods. According to one variant, the obtained decorative paper can be used outside of panels, such as in lamination assemblies in so-called CPL (compact laminates), which may consist of a laminate of two or more layers of paper impregnated with cured resin.

[0002] More specifically, the present invention relates to a method for manufacturing laminated panels, wherein the panels comprise at least a substrate material and a top layer having printed decorations thereon. The method can be used to manufacture panels whose top layer is formed of a thermosetting resin and one or more paper layers, wherein the paper layers include decorative paper having printed patterns. Background Technology

[0003] Traditionally, the decorations or patterns on such panels are printed onto paper using offset printing or rotary gravure printing. The resulting paper is used as decorative paper in so-called laminated panels. To manufacture such panels, the DPL (Direct Pressure Lamination) method can be used. According to the DPL method, the printed paper or decorative paper is provided with a melamine-based resin to form a decorative layer. A laminate is then formed comprising at least a sheet-like substrate, the decorative layer, and possibly a protective layer on top of the decorative layer, wherein the protective layer or overlay is also based on resin and / or paper. The laminate is subjected to pressing, and the pressing process results in the inter-linking or adhesion of the decorative paper, substrate, and protective layer, as well as the curing of the resin present in the laminate. As a result of the pressing operation, a decorative panel with a melamine surface is obtained, which can be highly abrasion-resistant. A counter layer or balancing layer can be applied to the underside of the sheet-like substrate, or alternatively, the decorative layer can also be attached to the underside, particularly in the case of laminated panels used for furniture. Such a opposing or balancing layer, or any other layer located on the underside of the laminate, restricts or prevents possible bending of the decorative panel and is applied in the same pressing process, for example, by providing a resin-bearing paper layer as the bottom layer of the stack, on the side of the stack opposite to the decorative layer. For an example of the DPL method, refer to EP 1 290 290, from which it is further known that an embossing is provided on the melamine surface during the same pressing process or pressing operation, i.e., by bringing the melamine surface into contact with a structured pressing element, for example, a structured pressing sheet.

[0004] Printing paper at an affordable price using analog printing methods, such as rotary gravure or offset printing, inevitably leads to large, low order volumes for specific decorative paper and limits achievable flexibility. Changes to decorations or patterns require approximately 24 hours of printing equipment downtime. This downtime is necessary for changing printing rollers, cleaning the printing equipment, and adjusting the colors of the new decorations or patterns to be printed.

[0005] Digital printing techniques, particularly inkjet printing, are becoming increasingly popular as an alternative to analog printing, whether on paper or directly on sheet-like substrates that may have an intermediate preparatory layer, for creating decorations or patterns. This digital technology significantly enhances the flexibility of decorative printing. Such techniques are disclosed in references to EP 1 872 959, WO 2011 / 124503, EP 1 857511, EP 2 431 190, EP 2 293 946, WO 2014 / 084787, WO 2015 / 124515, and WO 20518215.

[0006] EP 2 132 041 discloses a method comprising at least the steps of providing a paper layer having a thermosetting resin and providing said resin to provide a printed pattern for the paper layer. Preferably, a multi-color printed pattern is applied to the aforementioned paper layer to achieve decoration, for example, presenting a wood grain. This decoration extends to most, or even the entire, of the paper layer providing the resin. In EP 2 132 041, a digital printing press, particularly an inkjet printer, is used. However, it is difficult to reliably further process such printed paper to manufacture laminates, as in the DPL method, because pressing defects may originate from the resin surface, and milling, drilling, or sawing on the laminate surface or its edges often results in splitting in the top layer. Furthermore, the inks or dyes in EP'041 may over-wet the paper layer, causing wrinkling or bleeding during further processing of the printed paper, leading to an unstable and / or slow production process. To address this problem, EP'041 proposes immediately drying the printed paper layer.

[0007] EP 1 044 822, EP 1 749 676, and EP 2 274 485 disclose the use of inkjet receiver coatings to improve print quality on untreated substrate paper layers. These inkjet receiver coatings contain pigments and polymers such as polyvinyl alcohol. Despite the enhancement, the color density printed on this treated paper is still inferior to that of analog printing.

[0008] As acknowledged in WO 2015 / 118451, the use of paper treated with an inkjet receiver coating can cause malfunctions in printing equipment. Dust can be released from the inkjet receiver coating and have various adverse effects on critical components of the inkjet printer. For example, dust can clog one or more nozzles and cause printing defects. WO 2015 / 118451 proposes avoiding excessive bends, i.e., overly sharp bends, in paper used in printing equipment to minimize dust release.

[0009] During their personal research, the inventors also encountered the problem of dust release from the paper layer during subsequent impregnation, even after the paper layer had already been printed. The released dust could contaminate the resin bath, rollers, cameras, and other equipment inside or adjacent to the impregnation channel, leading to defects in the final product or the equipment used. Summary of the Invention

[0010] The primary objective of this invention is to provide an alternative decorative paper layer for use in methods of manufacturing panels with decorative surfaces, and, according to several preferred embodiments thereof, to address one or more problems present in the prior art. Detailed Implementation

[0011] Therefore, according to its first independent aspect, the present invention relates to a decorative paper layer comprising a base paper layer and a pattern formed by digitally applying ink to at least one surface of the base paper layer, characterized in that the ink penetrates from the surface to the core of the base paper layer to a depth equal to less than 30% of the thickness of the base paper layer, preferably at least 10% of the thickness of the base paper layer. Preferably, the thickness of the base paper layer is 50-200 μm, more preferably 60-130 μm. The pattern formed by the digitally applied ink preferably covers most or even the entire base paper layer. Preferably, on average, at least 1 g / m² is present in the printed area of ​​the base paper layer. 2 Or at least 2g / m 2 Ink load.

[0012] Obviously, the longitudinal edges of the base paper layer may remain unprinted or printed with technical images, such as location marks and / or marks for visual inspection of print quality.

[0013] Preferably, the decorative layer is rolled up and thus has a length that is virtually without end, for example, at least 1,000 meters, and / or the width of the decorative layer is preferably 1-4 meters, more preferably 1.6-2.2 meters.

[0014] Preferably, the ink is a water-based pigment ink. Especially when the ink is applied via inkjet printing, the applied ink may have a relatively high water content because jetting microdroplets, such as those with a volume of 65 pL or smaller, requires a low-viscosity ink. According to a preferred embodiment, the ink droplets used can be 1-10 pL, for example, 3 or 6 pL droplets.

[0015] Preferably, the base paper layer has an average air resistance of 25 seconds or less according to the Gurley method (Tappi T460). Low air resistance makes the base paper layer particularly suitable for resin impregnation. Thermosetting resins are preferred, as in the DPL method described above. Preferred thermosetting resins are melamine-based resins, such as melamine-formaldehyde resin.

[0016] Preferably, the base paper layer has a density of 60-85 g / m³. 2 The surface weight of the paper, of which 70 or approximately 70 g / m² 2 It is the preferred value.

[0017] The inventors have discovered that ink penetration into the depth of the substrate paper layer should be permitted, but not excessively. The permissible penetration aims to achieve a certain degree of ink bleeding in the horizontal direction, i.e., in the direction encompassing the paper surface. Horizontal bleeding can result in the final recorded dots being significantly larger than the expected recorded dot size based on the applied ink droplet volume, and more specifically, in the case of inkjet printers, larger than the expected size based on the ejected ink droplet size. Significant horizontal bleeding or dot gain leads to high color density in the resulting print and allows for the acquisition of vibrant colors with less ink applied to the substrate paper layer. Preferably, the ink is applied by ejecting ink droplets onto the substrate paper layer with a sharpness expressed in DPI (dots per inch) value, creating an average distance between the centers of adjacent dots formed by the respective ink droplets, and the dots formed by the ink droplets are larger than this average distance.

[0018] Preferably, the depth of ink penetration is less than 30 μm, more preferably 20 μm or less.

[0019] Limited ink penetration combined with significant horizontal bleeding or dot gain can be achieved by one, or a combination of two or more of the following possibilities.

[0020] According to the first possibility, silica particles can be used on the surface of the base paper layer. Preferably, the silica content of the base paper layer is substantially available on the surface. Preferably, the silica content of the base paper layer rapidly decreases below the surface. Preferably, the silica content of the base paper layer at a depth of 20% or even 10% of the thickness of the base paper layer is less than 5% of the silica content on the surface, or even less than 1% (if not 0%). Silica particles can be present in an ink receiving layer provided at the surface. Preferably, this ink receiving layer also contains a binder, preferably a hydrophilic binder, such as PVA (polyvinyl alcohol), and / or contains a metal salt, such as calcium chloride or CaCl2. The availability of silica particles directly on the surface of the base paper layer, possibly in combination with a hydrophilic binder, can lead to rapid absorption by the ink carrier and limited bleeding of the colored pigment dispersed in the carrier in the depth direction. The preferred availability of metal salts on the surface of the base paper layer can destabilize the dispersed pigment and tend to lock the pigment to the surface or its immediate vicinity, while allowing the carrier to penetrate further downwards.

[0021] According to a second possibility, silica particles can be used in and / or on the substrate paper layer. These silica particles are precipitated silica particles, preferably having a particle size expressed as a d50 particle size determined by laser scattering particle size analysis (DPS) of 1-40 μm, more preferably 1-15 μm, or 2-12 μm. In contrast to smaller particles, particles in the 1-40 μm range are less readily absorbed by the substrate paper layer upon application, thus remaining more effectively on the paper surface. Precipitated silica particles are generally larger than, for example, fumed silica particles and have a higher surface roughness. Precipitated silica is porous, and if the printed paper layer is subsequently impregnated with a resin such as melamine resin, the resin may also penetrate the pores of the precipitated silica. Moreover, precipitated silica contains more silanol groups and hydroxyl groups than fumed silica. These groups have a higher affinity and compatibility with resins such as melamine resin. The inventors further observed that, compared to the same coating formed with fumed silica, the coating obtained with precipitated silica exhibited a higher roughness, or in other words, a significantly lower BEKK smoothness value (measured according to ISO 5627:1995). All of these are particularly significant when using high ink loadings, such as 4 mL / m³. 2 When more or more ink loads form a pattern or certain areas thereof, any resin or resin layer applied on top of the printed pattern will adhere better.

[0022] According to a third possibility, the core of the substrate paper layer contains no or substantially no silica particles. Preferably, any silica-containing coating is preferably present primarily on the surface of the substrate paper layer, i.e., where it most effectively limits penetration depth and produces some horizontal bleeding or dot gain. The inventors have observed that some commercially available inkjet-printable substrate paper layers for DPL panels have a large content of relatively small, i.e., 200 nm or smaller fumed silica particles that penetrate between the cellulose fibers of the substrate paper layer. These papers result in a much greater degree of penetration of pigment-based water-based inks in the depth direction, leading to a subsequent loss of color density. Higher ink loads must be used to achieve a certain color density, which in itself causes adhesion problems with any resin to be applied to or on the printing paper layer. The inventors have observed that in these commercially available papers, especially when jetted with small ink droplets such as 3 pL ink droplets, horizontal bleeding may practically not exist.

[0023] Preferably, all three possibilities described above are combined on the surface of the same base paper. Preferably, the obtained base paper layer contains precipitated silica particles with a d50 particle size of 1-40 μm on one of its main surfaces, while the core of the paper layer contains no or substantially no silica particles.

[0024] Preferably, the smallest droplet size that can be ejected by the printing press exhibits a significant dot gain, for example, 10% or higher.

[0025] Preferably, the paper is treated such that ink droplets with a size of 5 pL exhibit a dot gain of 10% or higher.

[0026] Preferably, a 3 pL ink droplet, regardless of whether it is the smallest available, and having a theoretical droplet diameter of about 18 μm, is recorded as a dot with a diameter of at least 20 μm. In other words, the dot gain of the 3 pL ink droplet is preferably 10% or higher. A 6 μL ink droplet with a theoretical droplet diameter of about 22.5 μm is preferably recorded as a dot with a diameter of at least 35 μm or at least 40 μm. In other words, the dot gain of the 6 pL ink droplet is preferably 55% or higher, or 77% or higher. A dot gain of about 100% is not excluded, which means that the recorded size is twice or about twice the theoretical droplet diameter.

[0027] Dot gain preferably results in the diameter of the recorded dots being equal to or greater than the average distance between adjacent dots. This feature is important regardless of whether ink penetration is limited to 30% of the thickness of the base paper layer. Therefore, according to a second independent aspect, the invention also relates to a decorative paper layer (whether or not according to the first aspect), comprising a base paper layer and a pattern formed by digitally applying ink to at least one surface of the base paper layer, characterized in that the ink is applied by spraying ink droplets onto the base paper layer with a sharpness expressed in DPI (dots per inch) and producing an average distance between the centers of dots formed by each ink droplet, and the dots formed by the ink droplets are greater than the average distance and / or the dots formed by the smallest ink droplet used in the pattern are greater than the average distance. Preferably, at least the recorded dots of the smallest ink droplet exceed the average distance due to the aforementioned dot gain or horizontal bleeding, as described in the first aspect. In other words, although the theoretical diameter of the ink droplet may be smaller than the average distance, the dot gain preferably results in the diameter of the recorded dots being greater than the average distance. For example, the printed pattern can be provided by jetting ink droplets into the substrate paper layer at a resolution of 1200 DPI, where the smallest droplet has a volume of 3 pL. This results in an average distance between the centers of dots formed by each droplet of approximately 21 μm. Theoretically, a 3 pL droplet has a diameter of approximately 18 μm, which is smaller than the average distance between the center of the dots. Dot gain or horizontal bleeding is preferably configured such that the recorded dots have a diameter greater than 21 μm.

[0028] According to the features of the invention in the second aspect, particularly at low ink loading (e.g., 2 mL / m³), 2 When formed using halftone printing (or lower) and / or with halftone printing, the color density of the pattern is increased. In such patterns, the risk of obtaining grainy images or visually missing nozzle malfunctions is reduced by the present invention.

[0029] According to the alternative sharpness of the second aspect of the invention, the recorded dot diameter of the smallest ink droplet in the printed pattern is at least equal to the pitch of the nozzles in the applied printhead, that is, at least equal to the distance between adjacent nozzles in the applied printhead. Preferably, all nozzles of the printhead have nozzle openings of the same size. Preferably, the theoretical diameter of the smallest ink droplet is smaller than the pitch, but the recorded diameter of such droplet is equal to or greater than the pitch due to horizontal bleeding or dot gain on the surface of the substrate paper layer. When the nozzles of the printhead are arranged in a repeating series of two or more adjacent nozzles with different nozzle opening sizes, the sum of the recorded diameters of the ink droplets ejected from the series is preferably greater than the pitch between the two or more such series. For example, the nozzles can be arranged in alternating sizes. In this case, the series contains two types of nozzles, and the pitch is the distance between two large nozzles or two small nozzles. Preferably, the sum of the recorded diameters of the small nozzles and the large nozzles is greater than the distance between two large nozzles or two small nozzles.

[0030] Obviously, it is preferable to use a single ink droplet to record one dot, the so-called 1dpd (droplets per dot). When using multiple ink droplets, for example, when using grayscale or halftone printing to record dots, it is preferable that the diameter of the recorded dots is at least a multiple of the average distance and / or the nozzle spacing. Preferably, a maximum of 3 drops are used per dot. The ink droplets used to form a single dot may have different volumes, such as a combination of 6 pL drops and 3 pL drops. Using more drops per dot generally results in reduced ink consumption, a lower risk of visual nozzle failure, and a more homogeneous and uniform printed surface.

[0031] It is evident from the above that any coating on the surface of a printable paper layer is preferably concentrated on the surface, rather than within the cellulose component available for use in the paper layer, i.e., inside the paper layer. This is particularly problematic for a base paper layer suitable for subsequent resin impregnation, such as using thermosetting resins like melamine-based resins, i.e., for methods like the DPL. Such a base paper is porous and, in particular, characterized by low average air resistance, as expressed by its Glyfler value. To reliably obtain such a coating, the invention relates, according to a third independent aspect, to a method for manufacturing a printable paper layer, wherein the method comprises at least the following steps:

[0032] -Provide a base paper layer with a Glyce value of 25 seconds or less (measured according to Tappi T460);

[0033] - The step of applying a coating material to at least one surface of the base paper layer, wherein the coating material comprises at least an adhesive and a silica pigment;

[0034] The feature is that measures are taken to minimize the absorption of the coating material in the core of the base paper layer, said measures being any one, or a combination of two or more of the following:

[0035] The step of applying the coating substance is performed using coating equipment other than a sizing machine. Sizing machines are known in papermaking. In a sizing machine, the paper to be treated passes from top to bottom through the gap between two rolls. At the entrance of the gap, there may be a reservoir for the coating substance between the rolls, a so-called "flooded nid". The coating substance is absorbed into the paper as it passes through the reservoir. Due to the hydrodynamic and mechanical pressures applied by the rolls, the substance is forced into the cellulose core of the paper. According to the present third aspect of the invention, this should be avoided.

[0036] - The step of applying the coating material is performed without squeezing the coated paper. It is evident from the above that, while applying the coating material to the base paper layer, it is preferable to avoid squeezing the coating material or applying mechanical pressure to it, so as to minimize the penetration of the coating material into the cellulose core of the base paper layer.

[0037] The step of applying the coating material is carried out by a so-called membrane press. A membrane press is an example of a coating device that applies only minimal mechanical pressure to the coating material when applied to a base paper layer. In a membrane press, the paper to be treated passes from top to bottom through the nip of two rollers. One or two rollers, preferably only one, provide the coating material on their surface. The rollers then transfer the material into or near the nip on the paper surface. The amount of coating to be applied can be defined by the application of the material to the rollers, which can be metered, for example, since the application of the material to the rollers is done by a blade, wirebar, or the like. The absence of hydrodynamic pressure and the significantly lower mechanical pressure applied by the rollers minimize the amount of coating material pressed into the cellulose core of the paper. The application rollers may optionally be rubber-coated, for example, with a Shore A hardness of 30-80, to minimize the squeezing effect. Other coatings on the rollers, preferably with a Shore A hardness of 30-80, can also limit the squeezing effect.

[0038] The step of applying the coating material is performed by gravure roller, spraying, slot coating, curtain coating, anilox coating, pressure chamber coating, screen coating, and / or rotary screen coating, for example, by the so-called magnoroll of Zimmer Maschinenbau GmbH in Austria. Each of these coating devices, individually or in combination, forms an alternative to the aforementioned membrane press.

[0039] - The silica pigment is precipitated. As mentioned earlier, regarding the first aspect, precipitated silica pigments are generally larger than, for example, fumed silica pigments. Larger particle sizes tend to impregnate less into the cellulose core of the base paper layer.

[0040] The silica pigments have a size of 1 μm or larger, for example, up to and including 40 μm, defined by a d50 particle size value determined by laser scattering particle size analysis. Independent of the silica type, the larger the average particle size, the less they impregnate into the cellulose core. For a substrate paper layer with a Gurley value of 25 seconds or lower, a 1 μm d50 size is the minimum.

[0041] -The silica pigment has a content of 100-750m 2 / g, preferably 300-750m 2 The specific surface area per g is defined by the BET area as measured according to ISO 9277:2010. A higher BET area results in better pigment incorporation into other components of the coating material, such as into the binder. Better-incorporated pigments tend to remain on the paper surface rather than penetrate into the cellulose core, and also retain other components of the coating material on the surface.

[0042] As mentioned above, potential adhesion problems of resin or resin layers applied to the decorative paper layer may depend on the ink load in each area of ​​the printed pattern, or other characteristics of the pattern to be printed. To achieve a more flexible approach to resource and material consumption, according to a fourth independent aspect, the present invention relates to a method for manufacturing a substrate for a printable pattern, wherein the method includes at least the following steps:

[0043] - Steps for providing the basic substrate;

[0044] - The step of applying a coating material to at least one surface of the base paper layer, wherein the coating material comprises at least an adhesive and a silica pigment;

[0045] The feature is that the application of the coating substance is defined and / or controlled at least in part by the pattern.

[0046] Preferably, the coating material applied to specific areas of the surface is defined and / or controlled based on the expected ink load in those areas during subsequent digital printing steps. This can be done according to several examples, two of which will be further described below, without limitation.

[0047] According to the first example, the coating material can differ from one paper section to another, with each paper section providing a different printed pattern. For example, one paper section could be printed with a light wood grain pattern, while subsequent paper sections could be printed with a dark wood grain pattern.

[0048] According to the second example, which may or may not be combined with the first example, the coating material can vary within a paper section. For example, some sections of the paper section may be printed with a general light-colored wood grain pattern, while another paper section may be printed with darker parts of the same wood grain pattern, such as representing cracks or nuts, and the coating material will vary according to these sections.

[0049] According to a preferred embodiment of the fourth aspect of the invention, the coating material is controlled or defined by the pattern to be applied, which includes at least controlling or defining the amount of coating material applied to a specific area of ​​the paper surface, and therefore preferably controlling or defining the variation of said amount.

[0050] According to another preferred embodiment, which may or may not be combined with the foregoing preferred embodiments, the coating material is controlled or defined by the pattern to be applied, including at least controlling or defining the composition of the coating material applied to a specific area of ​​the paper surface, and therefore preferably controlling or defining variations in said composition. The composition of the coating can be varied, for example, by changing the mixing ratio between pigments, such as precipitated silica pigments and binders, such as PVA (polyvinyl alcohol), and / or by changing the availability of other components such as metal salts, and / or by changing the size or type of pigments, and / or by changing the binder (if available).

[0051] Preferably, the coating material is controlled such that in areas of the paper surface where a larger ink load is expected, thereby in darker printed areas, a higher water retention capacity is achieved, for example, by increasing the amount of coating material, increasing the size of the pigment, increasing the amount of pigment, and increasing the content of metal salts (if any).

[0052] Preferably, the printable paper layer obtained or available by the method of the third and / or fourth aspects of the invention has a BEKK smoothness of 150 seconds or less, preferably 100 seconds or less, on the surface on which the coating or ink receiving layer is applied, as determined according to ISO 5627:1995. As previously mentioned, this limited smoothness is beneficial for the lamination strength with subsequent resin layers applied on top of the printed pattern.

[0053] Preferably, this printable layer further exhibits the characteristics of the first and / or second aspects of the invention and / or its preferred embodiments when there is no printing on it.

[0054] Preferably, the printable paper layer comprises a coating including silica particles on at least one of its surfaces, while the core of the paper layer comprises a small amount and / or small particle size of silica particles and / or is substantially free of silica particles.

[0055] According to a fifth independent aspect, the present invention aims to minimize the risk of printing defects. To this end, the present invention relates to an ink for forming patterns by inkjet printing onto the surface of a paper layer, wherein the ink is water-based and / or contains 1 wt% to 40 wt% of insoluble matter and / or polymers, characterized in that the ink further contains a water-soluble, preferably organic, solvent with a boiling point above 120°C at atmospheric pressure. This solvent can be selected from a list consisting of alcohols, polyols, glycol derivatives, amines, and polar solvents. The total content of the solvent is preferably 5 wt% to 70 wt%, or 5 wt% to 50 wt%, preferably 5 wt% to 25 wt%.

[0056] Clearly, "insoluble" means "insoluble in the ink carrier at room temperature and atmospheric pressure." Similar to water-based inks, water is the preferred ink carrier.

[0057] Preferably, the ink contains 20wt%-40wt% of insoluble substances, such as at least pigments, and / or polymers, wherein the ink is preferably water-based. It is, of course, possible for the insoluble content to be less than 20%, or even less than 10%.

[0058] For water-based inks or inks containing a large amount of dispersed insoluble components or polymers, such as inks using pigment or resin microparticle dispersions, solvents such as water in the ink may evaporate from the nozzle during printing or while waiting for printing. This results in a decrease in the solvent concentration of the ink around the nozzle and an increase in ink viscosity. With increased ink viscosity around the nozzle, fluid resistance inside the nozzle increases, potentially leading to jetting malfunctions. Jetting malfunctions include fluctuations in the volume, flight time, or flight direction of the ejected ink droplets, or jetting termination due to, for example, nozzle clogging. Therefore, this can result in dot misalignment or incorrect dot size on the printing medium, or even no dots at all.

[0059] As a solution, the present invention, according to its fifth independent aspect, proposes to add a water-soluble, preferably organic solvent to the ink, which preferably has a boiling point above 120°C at atmospheric pressure. Specific examples of water-soluble organic solvents include alcohols (e.g., pentanol, hexanol, cyclohexanol, and benzyl alcohol); polyols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butanediol, glycerol, hexanediol, pentanediol, glycerol, hexanediol, and thiodiol); and ethylene glycol derivatives (e.g., ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, dipropylene glycol monomethyl ether, triethylene glycol monomethyl ether, propylene glycol monoethyl ether, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, propylene glycol dimethyl ether, dipropylene glycol dimethyl ether, tripropylene glycol dimethyl ether, tripropylene glycol dimethyl ether, tripropylene glycol dimethyl ether). Dimethyl ether, ethylene glycol diacetate, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, and ethylene glycol monophenyl ether; amines (e.g., ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, diethylenetriamine, triethylenetetramine, polyethyleneimine, and tetramethylpropylenediamine); and other polar solvents (e.g., formamide, N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, sulfolane, 2-pyrrolidone, N-methyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 2-oxazolidinone, 1,3-dimethyl-2-imidazolinone, triacetin, urea).

[0060] Water-soluble organic solvents can be used alone or in combination of two or more water-soluble organic solvents that are miscible in water without phase separation.

[0061] The total content of water-soluble organic solvents in inkjet ink is preferably 5wt%-70wt%, more preferably 5wt%-50wt%, and even more preferably 5wt%-25wt%.

[0062] It should be noted that the printable substrates obtained by the methods of the third and / or fourth aspects are preferably used for printing with water-based inks or possibly with UV-cured inks, latex-based inks, or water-UV inks. These substrates are initially intended for printing using inkjet printing equipment. However, the inventors have also found that using such treated paper in analog printing equipment, such as in rotary gravure printing using three or more rollers, improves print quality.

[0063] It should also be noted that when silica particles are applied to the surface of a base paper layer, in conjunction with any aspects mentioned in this invention, such silica particles can be silane-treated. Silane treatment of pigments can generally further enhance the reduction of dust release from the resulting inkjet receiver coating and the paper thus treated. Silane treatment can involve treatment with coupling agents such as aminoorganosilanes, hydroxysilanes, bipodial silanes, and / or other silanes. Preferably, the coupling agent is selected to reduce the risk of yellowing during aging of the resulting inkjet receiver coating. Preferably, the coupling agent comprises 0.1%-10% of the total wet weight of the inkjet receiver coating.

[0064] Preferably, any coating on the surface of the base paper layer, in addition to silica particles, preferably also contains an adhesive. Preferred adhesives for the inkjet receiving layer include polyvinyl alcohol (PVA), but depending on the variant, vinyl alcohol copolymers or modified polyvinyl alcohol may be used. Modified polyvinyl alcohol may be cationic polyvinyl alcohol, such as Kuraray's cationic polyvinyl alcohol grades, or Nippon Goshei's POVAL C506 and POVAL C118.

[0065] Any coating on the surface of the base paper layer, in addition to silica particles and possible adhesives, preferably contains one or more of the following agents:

[0066] - Crosslinking agent: 0.05-5g / m 2 Preferred concentration: 0.2-2 g / m 2 For example, a list consisting of aldehydes, polyaldehydes, dialdehydes, alcohols, boric acid, borax, polyols, urethanes, polyurethanes, carbonic acid, glyoxal-based reagents, zirconium-based reagents, and polycarbonates.

[0067] -Particle surface modifier or coupling agent: 0.05-5 g / m 2 Preferred concentration: 0.2-2 g / m 2 For example, a non-limiting list selected from aminosilanes, ureosilanes, aldehyde silanes, tetraethyl orthosilicate, silazanes, organically modified silanes, organically modified silazanes, chlorosilanes, organically modified chlorosilanes, bissilanes, organic bissilanes, silsesquioxanes, polysilsesquioxanes, silane oligomers, organically modified silane oligomers, bissilane oligomers, organically modified bissilane oligomers, oligomeric silsesquioxanes, and oligomeric polysilsesquioxanes.

[0068] - Additives: 0.005-2g / m 2 The preferred wetting agent is 0.05-1 g / m³. 2 Wetting agent; and / or defoamer 0.005-2g / m³ 2 Preferred concentration: 0.05-1g / m³ 2 Defoamer; and / or 0.005-2 g / m 2Preferred concentration: 0.05-1 g / m 2 bactericide.

[0069] Preferably, the base paper layer on which the coating is applied has a density of 50-100 g / m². 2 Basis weight, for example, 60-80 g / m³ 2 The base weight.

[0070] Preferably, in the case of paper layers, the side of the paper layer to which the coating or inkjet coating will be applied has been smoothed during its production (German: Smoothing reduces the amount of binder penetrating the core of the paper, allowing the pigments contained therein to be better bound by available binder substances, and potentially resulting in less variation in absorption. A printable paper layer, preferably obtained or available through the method of the present invention, including possible coatings, has a Gurley value of 30-120 seconds, preferably 30-80 seconds. Such a paper layer results in excellent print quality because deposited ink tends to penetrate less into the paper, and it is easier to achieve and maintain positional consistency, or so-called registration, between printed patterns applied using different inkjet heads. In fact, a relatively high Gurley value leads to greater paper dimensional stability because it is less hygroscopic. When impregnating with thermosetting resins on such high-Gurley paper, it is advisable to reduce the speed of the impregnation channel, use pressure impregnation techniques, and reduce the viscosity of the impregnation resin.

[0071] The coating available on the paper surface can be applied in a single step, or alternatively, according to the most preferred embodiment, the coating is applied in at least two sub-steps, wherein a first layer is applied using a first component and a second layer is subsequently applied using a second component, both compositions containing at least the adhesive.

[0072] The inventors have demonstrated that applying the coating in two separate steps results in better pigment incorporation or adhesion. The risk of dust release from the paper is reduced compared to applying the same amount of pigment in only one coating step. According to the inventors, this unexpected effect is attributed to the first layer forming a barrier that prevents the adhesive of the second layer from penetrating into the paper layers. The adhesive of the second layer is more effective at bonding the pigment, which would otherwise be loose or poorly adhered to the paper surface. Better pigment embedding leads to a significant reduction in dust release from the paper during further processing, such as printing or resin impregnation.

[0073] Applying the coating in both steps can further result in a more uniform application of the entire inkjet receiving coating obtained in this way. In cases where the first composition may be partially absorbed into the paper layer in an uneven manner and thus may result in an uneven first layer with less effective portion, the second composition at least partially balances the possible unevenness.

[0074] Applying the inkjet receiving coating in at least two steps allows for the creation of gradients in the thickness of the coating due to certain components, since the first and second compositions can have different components or can both have components present at different concentrations, as will be explained further. Applying the inkjet receiving coating in at least two steps also allows for the creation of coatings of varying thicknesses.

[0075] The method of the present invention, and especially those embodiments in which the inkjet receiver coating is applied in two steps, is particularly interesting when it begins with a paper layer having a low average air resistance, for example, a Glyph value equal to or less than 30 seconds, such as 25 seconds or less. In this case, the binder contained in the first layer tends to be largely absorbed into the paper, leaving most of the pigment content unbonded on the surface. Preferably, the paper layer is standard printing base paper or another untreated paper layer having an average air resistance of 30 seconds or less, expressed in Glyph values. Of course, it is not excluded that, according to alternative embodiments, the method of the present invention begins with paper treated with a thermosetting resin before the application of the inkjet receiver coating. Preferably, in the latter case, the paper layer providing the resin has an average air resistance of 100 seconds or less. Also in this case, applying the inkjet receiver coating in two steps has significant advantages regarding, for example, minimizing dust release, minimizing vertical bleeding of the jet ink, and uniform application of the inkjet receiver coating.

[0076] Typically, the method of the present invention, when the inkjet receiving coating is applied in two steps, allows for the application of an inkjet receiving coating with a higher pigment content, and thus a higher absorption capacity or a higher absorption rate to absorb the carrier of the applied ink, such as water in the case of water-based pigment inks, while retaining or even reducing dust released from the treated printable surface. The higher capacity or speed of carrier absorption can result in higher print sharpness.

[0077] Preferably, when the inkjet receiving coating is applied in two steps, the first layer and the second layer differ in that they exhibit one or more of the following properties:

[0078] 1. The first layer and the second layer contain the properties of pigments and binders, although the ratio of pigment to binder is different;

[0079] 2. The material used for the first layer and the second layer has a different dry weight characteristic;

[0080] 3. The first layer and the second layer contain the properties of pigments and binders, wherein the average particle size of the pigments in the first layer is greater than the average particle size of the pigments in the second layer;

[0081] 4. The first and second layers contain the properties of ink reactive compounds, although their compositions differ;

[0082] 5. The first layer contains at least pigment and binder, while the second layer contains no pigment, or contains at least less pigment than the first layer, or contains less than 10% pigment of the first layer.

[0083] Regarding the first-mentioned characteristic, it is preferable that the pigment-to-binder ratio of the first composition is greater than that of the second composition. In this way, the binder in the second layer primarily binds the pigment in the first layer and balances the inhomogeneities in the first layer.

[0084] Preferably, the pigment to binder ratio in the second composition is less than 2:1, and more preferably between 0:1 and 2:1. When the ratio in the second composition is less than 1.5:1, extremely low dust release has been demonstrated. As mentioned above, it is not excluded that in some embodiments, the second composition does not contain pigment.

[0085] Regardless of whether it is combined with the preferred second composition described above, the ratio of pigment to binder in the first composition can be selected as 1:1-25:1 or 2:1-10:1, preferably 3.5:1 or greater than 3.5:1, even more preferably 5.5:1 or greater than 5.5:1, but preferably less than 10:1.

[0086] A good combination of the first and second compositions is achieved when the pigment-to-binder ratio in the second composition is 0:1 to 2:1 and the pigment-to-binder ratio in the first composition is 3.5:1 to 10:1. However, it is apparent that, within the scope of this invention, the pigment-to-binder ratios in the first and second compositions can be equal or substantially equal.

[0087] Regarding the second mentioned characteristic, it is certainly not excluded that the same dry weight is applied to both layers. However, in this case, it is preferable to apply different pigment to binder ratios in the first and second compositions. Preferably, for each of the two layers, 0.5-5 g / m 2 And even better, 0.8-4.5g / m 2 The dry weight of the material is applied to the paper layers. When the dry weights of the materials used for the first and second layers differ, the first layer preferably comprises the material with the highest dry weight, for example, at least 20% more than the second layer. The composition of each layer preferably contains 12wt%-20wt% solids, such that, based on the wet weight of the layer, it preferably has a density of 4-23 g / m³. 2 The wet coating material is applied to the paper layer.

[0088] Regarding the third characteristic mentioned, larger pigment particles are preferably included in the first composition. Using large particles in the first layer provides excellent absorption by the ink carrier, while using small particles in the second layer provides a balancing effect and effectively reduces dust release from the paper surface. Preferably, in this case, the pigment particles in the first composition have an average particle size of 1-20 μm. Preferably, the pigment particles in the second composition have an average particle size of 100 nm-1 μm. Of course, it is generally not excluded that the first and second compositions may contain pigment particles with similar or identical average particle sizes.

[0089] Regarding the fourth characteristic mentioned, the second layer preferably contains a higher amount of the ink reactive compound than the first layer. The availability of the ink reactive compound in the upper coating layer results in effective interaction with the pigment in the jetted ink droplets. The ink reactive compound preferably contains a flocculant or another ink stabilizer, such as a cationic metal salt.

[0090] Preferably, the adhesives in the first and second compositions are the same, or at least the main components of the adhesives are the same. As previously mentioned, the main component is preferably polyvinyl alcohol.

[0091] Preferably, the paper obtained by the method of the present invention is provided with a thermosetting resin, such as melamine resin, after a printed pattern has been provided to it by inkjet printing. For this purpose, the paper layer is preferably coated only on one side, i.e., on the side provided for printing. The other side is preferably left untreated, so that the other side exhibits the original porosity of the paper layer from which it originates. The resin can then be provided substantially from the bottom side into the paper core. To allow the paper with the inkjet receiving coating to be fully impregnated, the speed of the impregnation channel can be reduced, the viscosity of the resin can be lowered, the impregnation can be pressurized, and / or the resin can be heated, for example, to 45-100°C, preferably 45-70°C.

[0092] According to one variant, the paper obtained using the method of the present invention is provided with a water-based polyurethane dispersion resin, an acrylic dispersion resin, and / or a latex dispersion resin, or a mixture of two or more of these resins, or a mixture of one or more of these resins with an amino plastic resin such as melamine resin. Preferably, the resin is provided to the paper after a printed pattern has been provided to the paper by inkjet printing. In the case of polyurethane or acrylic dispersion resins, the inventors have found that nonionic or cationic dispersions are preferred. These dispersions have been found to be more compatible with the treated paper and have a reduced risk of flocculation upon contact with the paper. This is particularly true in the case where the ink receiving layer contains metal salts such as CaCl2. As will be apparent from the foregoing, according to a specific independent aspect, the present invention relates to the use of cationic or nonionic dispersions, preferably polyurethane, latex, or acrylate, for coating and / or impregnating printable layers or printable substrates, or decorative paper layers, whether or not according to any aspect relating to the printable layer, decorative layer, or method of manufacture thereof described herein. This dispersion is preferably used to process paper layers containing inkjet receiver coatings, and preferably contains at least a metal salt, such as CaCl2 or MgCl2, and / or a paper layer with an inkjet receiver coating type having a pH value below 5.

[0093] Preferably, the inkjet receiving coating is deposited on the paper layer and preferably forced to dry, for example, in a hot air furnace or by infrared or near-infrared light or by microwave drying of a liquid substance.

[0094] The deposition of the liquid substance for the coating or ink receiving coating can be performed in the immersion channel or alternatively on the printing equipment immediately before the printing operation. The latter addresses any potential issues related to the limited shelf life of the inkjet receiving coating. Preferably, the liquid substance is deposited while the base paper layer is still in an "endless" shape, i.e., taken from a roll and not cut. This technique allows for a more uniform application of the inkjet receiving coating. Where the coating is completed entirely or partially on the printing equipment, the printing equipment is preferably a roll-to-roll or roll-to-plate printing press, including printheads, such as roll coaters, and / or coating equipment upstream of other printheads suitable for printing the liquid substance for the various sub-layers of the inkjet receiving coating. Such other printheads, for example, a row of other printheads, can have nozzles with a larger diameter than the nozzles used for the actual printed pattern. A resolution of 1-100 dots / inch, or even 1-25 dots / inch, is sufficient for these nozzles. The larger diameter allows for the jetting of a more viscous substance. This resolution can be sufficient for embodiments according to the third independent aspect mentioned in the invention, where the step of applying the coating substance is at least partially defined and / or controlled by the printed pattern to be obtained.

[0095] The liquid material used for the inkjet receiving coating preferably exhibits a Din cup 4 viscosity of 10-75 seconds at 20°C. This characteristic allows the liquid material to be applied directly to the surface of a paper layer or foil. In experiments, a solid content of 10%-30%, for example, about 12%, and a viscosity of 20-30 seconds, for example, about 24 seconds, will produce a sufficiently uniform coating on previously untreated paper layers, for example, when applied by a roll coater.

[0096] According to its sixth independent aspect, the invention also relates to a method of manufacturing a laminated panel, wherein the panel comprises at least a substrate material and a top layer having printed decoration thereon, wherein the top layer is formed substantially of a thermosetting resin, polyurethane, acrylic or latex dispersion resin, and one or more paper layers, wherein the paper layers comprise decorative paper layers and / or printable paper layers printed according to any other aspect of the invention.

[0097] Obviously, the decorative paper layer can be used in a method of manufacturing a panel with a decorative surface, wherein the panel comprises at least a substrate and a top layer containing a thermosetting resin, wherein the top layer comprises a paper layer with a printed pattern, characterized in that, in order to provide said portion of said printed pattern, pigment-containing ink is used to deposit on said substrate paper layer or printable paper layer by a digital inkjet printer, and characterized in that the total dry weight (and preferably also wet weight) of said pigment-containing ink deposited on said paper layer is 9 g / m³. 2 Or lower, preferably 3-4 g / m 2 Or even lower, where water-based or so-called water-based inks are used for the pigment-containing inks. The imposed limitation on ink dry weight results in a reduced risk of printing defects and top-layer splitting in the ink layer. In practice, the potential interference between the ink layer and the thermosetting resin during the pressing operation is limited. This is due to the ink loading being limited to a maximum of 9 g / m³. 2 This allows for controlled paper wrinkling or swelling due to ink, ensuring stable further processing. Preferably, organic pigments are used for the pigment-containing ink. Organic pigments are known to be more stable when exposed to sunlight or other ultraviolet radiation sources. Preferably, the pigment in the pigment-containing ink has an average particle size of less than 250 nm. Preferably, the dry weight of the deposited pigment-containing ink is 5 g / m³. 2 Or even smaller, for example, 4 or 3 g / m³ 2 Or even smaller. Preferably, the printed pattern is entirely or at least substantially composed of this pigment-containing ink, wherein the printed pattern covers most of the paper layer, preferably 80% or more of the surface. Preferably, the total volume of the deposited pigment-containing ink is less than 15 mL, or even better, less than 10 mL or less, for example, 5 mL or less.

[0098] Preferably, the base paper layer of the present invention is opaque and / or contains titanium dioxide as a whitening agent.

[0099] Preferably, the printed patterns applied to the printable paper layer of the present invention and / or contained in the decorative paper layer of the present invention cover most of the paper layer, preferably 80% or more of the surface.

[0100] Preferably, before or after printing, and before or after applying the inkjet receiving coating, the base paper layer is provided with a thermosetting resin in an amount equal to 40%-250% of the dry weight of the resin relative to the weight of the paper. Experiments have shown that the resin applied within this range provides sufficient impregnation of the paper, thereby largely preventing cracking and stabilizing the paper dimensions to a high degree.

[0101] Preferably, before or after printing, and before or after applying the inkjet receiving coating, the base paper layer is provided with an amount of thermosetting resin such that the core is at least saturated with resin. This saturation can be achieved when the amount of wet resin provided corresponds to at least 1.5 or at least 2 times the paper weight. For example, a paper with a surface weight of 70 g / m²... 2 The paper can be 140g / m 2 This involves applying wet resin at twice the weight of the paper to produce 140 g / m² of resin upon drying. 2 The paper is treated to have a saturated core. It should be apparent that the resin provided on the paper layer is not necessarily only used for the core of the paper, but can also form a surface layer on both flat sides of the paper. An inkjet receiving coating can then be present on the surface of the paper, with such a thermosetting resin surface layer in between. According to a specific embodiment, the paper layer is first impregnated or saturated, then the resin is removed at least partially on the side to be printed, and the coating or inkjet receiving coating is provided, if possible.

[0102] Preferably, the obtained paper layer providing the resin, i.e., after providing the thermosetting resin, has a relative humidity of less than 15%, and more preferably 10 wt% or less.

[0103] Typically, paper and inkjet receiving coatings, whether or not resin is provided, are printed at a relative humidity of less than 15%, with 10% or lower being preferred.

[0104] Preferably, the step of providing the thermosetting resin to the paper layer includes applying a mixture of water and resin to the paper layer. Applying the mixture may include immersing the paper layer in a bath of the mixture and / or spraying, jetting, or otherwise coating the mixture onto the paper. Preferably, the resin is provided in a metered manner, for example, by using one or more squeeze rollers and / or surgical blades to set the amount of resin added to the paper layer.

[0105] Preferably, the thermosetting resin is a melamine-based resin, more specifically a melamine-formaldehyde resin with a formaldehyde to melamine ratio of 1.4-2. This melamine-based resin is a resin that undergoes condensation polymerization when exposed to heat during pressurization. The condensation reaction produces water as a byproduct. The present invention is particularly relevant for these types of thermosetting resins, i.e., those that produce water as a byproduct. The water produced, as well as any residual water in the pre-pressed thermosetting resin, must be largely removed from the cured resin layer before it is trapped and causes the hardened layer to lose transparency. While available ink layers can hinder the diffusion of vapor bubbles to the surface, the present invention provides measures to limit this barrier. An inkjet receiving coating is advantageous in this regard because it provides an additional buffer to capture such escaping vapor. When using porous and / or hydrophilic inkjet receiving coatings, such as those using silica and / or polyvinyl alcohol, some water vapor generated during the curing of the thermosetting resin in the printing press may be absorbed by this coating, making the process less prone to pressing defects, such as water vapor trapped in bubbles. Other examples of such thermosetting resins that lead to similar condensation reactions include urea-formaldehyde resins and phenol-formaldehyde resins.

[0106] Preferably, the paper layer is impregnated with resin only after the inkjet receiving coating is applied and after printing. In this way, the inkjet receiving coating is completely unaffected by the water contained in the water-resin mixture used for impregnation.

[0107] It is evident from the above that the method of the sixth aspect of the present invention preferably includes the step of hot-pressing a resin-providing paper layer to at least cure the resin in the obtained resin-providing decorative paper. Preferably, the method of the present invention constitutes part of the DPL method as described above, wherein the printed resin-providing paper layer of the present invention is accepted in a laminate and pressed as a decorative layer. Of course, it is not excluded that the method of the present invention will constitute part of the CPL (Compact Laminate) or HPL (High Pressure Laminate) method, wherein the decorative layer is at least hot-pressed with a core paper layer impregnated with a variety of resins, such as so-called kraft paper, forming a substrate under the decorative layer, and wherein the obtained pressed and cured laminate or laminate, in the case of HPL, is glued to another substrate, such as particleboard or MDF or HDF board.

[0108] Obviously, generally, and / or according to the sixth aspect of the invention, any type of substrate material can be used, such as the aforementioned particleboard, MDF, HDF board, or board containing thermoplastic materials, or mineral board. The board containing thermoplastic materials can be a closed-cell foamed PVC board that may contain fillers, or a solid, i.e., non-foamed PVC board that may contain fillers, wherein the filler content may or may not exceed 50 wt% of the core material. Such fillers can be mineral fillers, such as chalk or lime, or organic fillers, such as wood, bamboo, grass, etc. The mineral board can be a water-cured board or a pressed board. The mineral board can be a gypsum board, fiber cement board, or another cement board such as a magnesium oxide-based board, for example, cured by reacting with magnesium chloride and / or magnesium sulfate.

[0109] Preferably, after printing, a further resin layer is applied over the printed pattern by, for example, a cover layer, i.e., a carrier layer providing resin, or a liquid coating, preferably when the decorative layer is laid on the substrate (loosely or already attached or adhered thereto).

[0110] The base paper layer of the present invention can be a colored, tinted, and / or dyed base paper. The use of a colored and / or dyed base layer can further limit the dry weight of the deposited ink to obtain a specific pattern or color. In the case of paper, it is preferable to add the dye or pigment to the pulp before forming the paperboard. Alternatively, the ink receiving coating on the base paper layer to be printed is colored or tinted using colored pigments. However, according to general disclosures, the pigment contained in the inkjet receiving coating is preferably colorless or white.

[0111] Preferably, for printing the paper layers or foil of the present invention, a digital inkjet printer that allows ink droplets with a jet volume of less than 50 picoliters is used. The inventors have found that working with ink droplets having a volume of 15 picoliters or less, for example, 10 picoliters, provides a considerable advantage in limiting the dry weight of the deposited ink. The preferred digital inkjet printer allows for a resolution of at least 200 dpi, or even better, at least 300 dpi (dots per inch). The preferred digital inkjet printer is of the single-pass type, wherein the printed pattern is provided to the paper layer in a single, continuous relative movement of the paper layer with respect to the printing press or printhead. The use of other digital inkjet printers, such as so-called multi-pass or plotter-type printers, is not excluded. For single-pass printers, and at least in some cases for multi-pass printers, the printhead preferably extends across the entire width of the paper to be printed. This is not the case with plotters or some multi-pass designs where the printhead needs to perform scanning movements in the width direction of the paper layer. However, the use of such printers in the method of the present invention is not excluded. It is important to note that a key advantage of multi-pass printing presses is that any faulty nozzle can be masked by subsequent passes. In this type of press, the nozzle can drift slightly between passes, resulting in multiple nozzles printing at specific locations on the paper dot. Using multi-pass equipment, or even a plotter, it is possible to perform automated maintenance or cleaning between subsequent passes when needed. The problem of nozzle failure is particularly relevant when using water-based or so-called water-based pigment inks. In fact, nozzles can become clogged by ink pigments because the water has dried out. However, the fourth aspect of this invention seeks to provide a solution to this problem, or at least mitigate these problems.

[0112] Obviously, according to the most preferred embodiment of the invention, the paper layer remains flexible during printing, and the paper layer is only attached to or placed on the sheet-like substrate after printing. According to variations, the paper layer is already attached to or loosely placed on the sheet-like substrate during printing. Possible adhesion to the substrate can be achieved using urea-based, phenol-based, melamine-based, polyurethane-based adhesives, and similar adhesives. Such adhesion can be achieved by pressing, regardless of whether hot pressing is performed.

[0113] Preferably, the method of the sixth aspect of the invention further includes the step of applying a counter layer or balancing layer to the surface of a substrate opposite to the printed paper layer. In the case of a paper-based decorative layer, the counter layer or balancing layer preferably comprises a paper layer and a thermosetting resin, preferably the same resin as the top layer.

[0114] Preferably, the adhesion of the plate-like substrate, possible opposing layers, and possible transparent or translucent layers to each other is achieved in a single pressing process. According to the most preferred embodiment of the sixth aspect, these steps are accepted within the DPL method process.

[0115] According to the most important example of the present invention, it has 60-90 g / m 2 Standard printing paper of a certain weight, such as printing paper for rotary gravure printing, is provided with an inkjet receiving coating according to the second aspect of the invention, and wood grain is printed on it using a digital inkjet printer employing water-based pigment inks. Melamine resin is then provided to the printed paper layer through a standard impregnation channel; i.e., through rollers, impregnation, jetting, and / or spraying equipment. The resin-provided paper layer is then dried until a residual moisture content of less than 10%, preferably about 7%, is reached. A so-called overlay is formed by the resin-providing opposing layer, a sheet-like substrate, the resin-providing paper layer, and the resin-providing paper layer. The laminate is then pressed at a temperature of about 180-210°C and a pressure greater than 20 bar, for example, 38 bar, for a period of less than 30 seconds. During pressurization, the surfaces of the laminate contact a structured pressing element, such as a structured pressing plate, and an embossing is formed in the top layer of the resulting laminate. The resulting embossing can be formed to align with the printed pattern of the resin-providing paper layer.

[0116] It is further apparent that the decorative paper layer of the first aspect, or the decorative paper layer obtained in the second and / or third aspects of the invention, is suitable as decorative paper or, respectively, as decorative foil in methods of manufacturing floor panels, furniture panels, ceiling panels and / or wall panels.

[0117] Obviously, during the method of the present invention, it may be necessary to divide the aforementioned printable paper layers and / or decorative paper layers to obtain their respective final dimensions. Panels obtained by DPL pressing or similar processes are preferably sawed or otherwise divided. Other processing of the obtained panels is, of course, not excluded.

[0118] It is further apparent that once printed and obtained or available through one or more of the described aspects or their preferred embodiments, the paper layer is preferably further applied by a DPL pressing process. However, several alternative application methods may also be implemented. For example, such a paper layer, preferably after printing, can be glued to a substrate and finished by acid curing, UV curing, or electron beam curing of a clear varnish.

[0119] This invention is by no means limited to the embodiments described above, but such methods, decorative paper layers or printable substrates can be implemented in various variations without departing from the scope of this invention.

Claims

1. A decorative paper layer comprising a base paper layer and a pattern formed by digitally applying ink to at least one surface of the base paper layer, characterized in that, The ink penetrates from the surface into the core of the base paper layer to a depth equal to less than 30% and at least 10% of the thickness of the base paper layer. Silica particles are available on the surface of the base paper layer. The silica content at a depth of 10% of the thickness of the base paper layer is less than 1% of the silica content on the surface. The silica particles are precipitated silica particles with a density of 1-40. The particle size, expressed as d50 particle size by laser scattering particle size analysis, is μm. The silica particles are present in an ink receiving layer provided on the surface. The core of the base paper layer is free of silica particles. The ink receiving layer also contains a metal salt of calcium chloride. The ink is applied by spraying ink droplets onto the base paper layer with a sharpness expressed in dots per inch, producing an average distance between the centers of the dots formed by each droplet, and the dots formed by the ink droplets are greater than the average distance. The decorative paper layer with the ink receiving layer has an average air resistance expressed in Glyfler values ​​of 30-80 seconds. The ink receiving layer comprises a first layer and an upper second layer. The first layer contains at least pigment and binder, while the second layer does not contain pigment. The silica particles have a size of 300-750 μm. 2 / g is the specific surface area defined by the BET area measured according to ISO 9277:2010.

2. The decorative paper layer according to claim 1, characterized in that, The thickness of the base paper layer is 50-200 μm.

3. The decorative paper layer according to any one of claims 1 to 2, characterized in that, The depth is less than 30 μm.

4. The decorative paper layer according to claim 1, characterized in that, The precipitated silica particles have a particle size of 1-15 μm, expressed as a d50 particle size determined by laser scattering particle size analysis.

5. The decorative paper layer according to claim 1, characterized in that, The thickness of the base paper layer is 60-130 μm.

6. The decorative paper layer according to any one of claims 1 to 2, characterized in that, The depth is 20 μm or less.

7. The decorative paper layer according to claim 1, characterized in that, The precipitated silica particles have a particle size of 2-12 μm, expressed as a d50 particle size determined by laser scattering particle size analysis.